Method and system for using a database and gps position data to generate bearing data

ABSTRACT

A method and system for providing a bearing from a vehicle to a transmitting station are described. The method includes accessing a database to obtain transmitter position information for the transmitter, obtaining vehicle position information based on a GPS signal, and generating the bearing from the vehicle to the station utilizing the transmitter position information and the vehicle position information. The system includes a database storing transmitter position information identifying a position of the transmitter, a GPS receiver obtaining vehicle position information identifying a current position of the vehicle based on a GPS signal, and a controller generating a bearing from the vehicle to the transmitter utilizing the transmitter position information and the vehicle position information.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 10/818,900, filed Apr. 6, 2004, which in turn is acontinuation-in-part of U.S. application Ser. No. 10/736,969, now U.S.Pat. No. 7,337,063, filed Dec. 16, 2003. The above-identifiedapplications are hereby incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

The present invention relates generally to aircraft navigation andlanding. More specifically, embodiments of the invention relate tomethods and systems for navigating and landing aircraft.

A VHF (very high frequency) Omni-directional Range (VOR) navigationsystem is implemented by dispersing VOR transmitter facilities across ageographic area. VOR receivers are located on aircraft which navigatethrough such a geographic area. The basic principle of operation of theVOR navigation system includes transmission from the VOR transmitterfacilities transmitting two signals at the same time. One VOR signal istransmitted constantly in all directions, while the other is rotatablytransmitted about the VOR transmission facility. The airborne VORreceiver receives both signals, analyzes a phase difference between thetwo signals, and interprets the result as a radial to or from the VORtransmitter 100. The VOR navigation system allows a pilot to simply,accurately, and without ambiguity navigate from VOR transmitter facilityto VOR transmitter facility. Each VOR transmission facility operates ata frequency that is different from surrounding VOR transmitters.Therefore a pilot can tune their VOR receiver to the VOR transmissionfacility to which they wish to navigate. Widely introduced in the 1950s,VOR remains one of the primary navigation systems used in aircraftnavigation.

The rotating transmission signal is achieved through use of a phasedarray antenna at the VOR transmission facility. Separation betweenelements of the array causes nulls in the signal received at theaircraft. Element separation may also cause erratic signal receptionwhen an aircraft is within an area above the antenna array. Such nullsresult in a conically shaped area originated at the VOR transmitter andextending upward and outward at a known angle. The conically shaped areais sometimes referred to as a cone of confusion. When an aircraft iswithin the cone of confusion, a pilot typically navigates utilizing onlyheading information, a process sometimes referred to as dead-reckoning.It is advantageous for a pilot to know that he or she is entering thecone of confusion.

An instrument landing system (ILS) also includes ground basedtransmitters, located at runways, and airborne receivers. The ILStransmitters transmit signals, received by the receivers on theaircraft, which are utilized to align an aircraft's approach to arunway. Typically, an ILS consists of two portions, a localizer portionand a glide slope portion. The localizer portion is utilized to providelateral guidance and includes a localizer transmitter located at the farend of the runway. The glide slope portion provides vertical guidance toa runway and includes a glide slope transmitter located at the approachend of the runway. More specifically, a localizer signal providesazimuth, or lateral, deviation information which is utilized in guidingthe aircraft to the centerline of the runway. The localizer signal issimilar to a VOR signal except that it provides radial information foronly a single course, the runway heading. The localizer signal includestwo modulated signals, and a null between the two signals is along thecenterline path to the runway.

The glide slope provides vertical guidance to the aircraft during theILS approach. The glide slope includes two modulated signals, with anull between the two signals being oriented along the glide path angleto the runway. If the aircraft is properly aligned with the glide slopesignal, the aircraft should land in a touchdown area of the runway. Astandard glide slope or glide path angle is three degrees fromhorizontal, downhill, to the approach-end of the runway. Known flightguidance systems, sometimes referred to as flight control systems, areconfigured to assume a nominal glide path angle, for example, threedegrees. Some known flight guidance systems have difficulty capturingthe null in the glide slope signal at runways whose glide path anglevaries significantly from the assumed glide path angle.

The VOR, localizer, and glide slope all provide an angular deviationfrom a desired flight path. The angular deviation is the angle betweenthe current flight path and the desired flight path. Depending on adistance from a transmitter, a linear change to the flight path tocorrect an angular deviation can vary widely. A linear deviation is thecurrent distance between the current flight path and the desired flightpath. Furthermore, most flight guidance systems are better suited toreceive and process linear deviations from a desired flight path. Knownflight guidance systems utilize data from distance measuring equipment(DME) and radar altimeters to convert angular deviations in one or moreof VOR, localizer, and glide slope, into linear deviations that can beacted upon by a pilot or a flight guidance system. Therefore, aircraftnot equipped with DME or a radar altimeter are not able to convert theangular deviations into linear deviations that can be optimally actedupon by the flight guidance system.

Known flight guidance systems utilize distance information from DME toestimate a distance to a VOR transmitter. The estimated distance, alongwith an angular deviation as determined from the VOR bearing is utilizedto determine a linear deviation from a desired flight path and detect acone of confusion. However, this approach assumes a default VORtransmitter station elevation, that the aircraft is equipped with DME,and that a DME station is co-located with the VOR transmitter.

Known flight guidance systems also utilize altitude information from,for example, a radar altimeter to estimate localizer deviations. Thealtitude, along with an angular deviation as determined by the localizerreceiver is utilized along with an assumption of runway length todetermine a localizer linear deviation from a desired flight path. Forglide slope linear deviations, the altitude, an angular deviation asdetermined by a glide slope receiver, and an assumed glide path angleare utilized to estimate the linear deviation from a desired glideslope. These estimations assume that the aircraft is equipped with analtitude measuring device (e.g. radar altimeter). It would beadvantageous to utilize actual data relating to VOR, localizers, glideslopes, and runway lengths and altitudes when providing a pilot or anauto pilot system navigation data. Similarly, it would be advantageousto provide such navigation data in aircraft which are not equipped withradar altimeters or DME.

In addition, known flight guidance systems are not able to properlycapture the localizer signals under conditions of high ground speeds andhigh intercept angles, due to the limited beamwidth of the transmitterand saturation of the localizer receiver at the necessary aircraftpositions. This results in late captures and potentially significantovershoot in acquiring the proper course.

Further, known flight guidance systems also do not track the selectedVOR course while traversing the “cone of confusion”, depending onmaintaining the aircraft heading at the time the cone of confusion isentered. This may result in significant tracking errors when the VORsignal is re-acquired upon exiting the cone, especially if wind changesor selected course occur during passage of the VOR station.

BRIEF DESCRIPTION OF THE INVENTION

In one embodiment of the present invention, a method for providing abearing from a vehicle to a transmitting station is provided. The methodcomprises accessing a database to obtain transmitter positioninformation for the transmitter, obtaining vehicle position informationbased on a GPS signal, and generating the bearing from the vehicle tothe station utilizing the transmitter position information and thevehicle position information.

In another embodiment of the present invention, a system for providing abearing signifying a deviation of a vehicle from a desired course isprovided. The system comprises a database storing transmitter positioninformation identifying a position of a transmitter transmitting bearingsignals to the vehicle, a GPS receiver obtaining vehicle positioninformation identifying a current position of the vehicle based on a GPSsignal, and a controller generating a bearing from the vehicle to thetransmitter utilizing the transmitter position information and thevehicle position information.

In still another embodiment of the present invention, a computer programproduct embodied on a computer readable medium for determining a bearingfrom a vehicle to a transmitter is provided. The computer programproduct comprises a data reception source code segment receiving datarelating to a position of the vehicle as determined from one or morepositioning sensors and a database access source code segment retrievingdata from a database relating to a position of the transmitter. Thecomputer program product also comprises a determination source codesegment determining a bearing from the vehicle to the transmitterutilizing the data relating to vehicle position and the data relating totransmitter position.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and features of the invention noted above are explained inmore detail with reference to the drawings which form a part of thespecification and which are to be read in conjunction therewith, and inwhich like reference numerals denote like elements in the various views.

FIG. 1 is a block diagram of a portion of a flight guidance systemaccording to one embodiment of the present invention.

FIG. 2 is a diagram illustrating a number of parameters utilized incalculating a linear deviation from a desired path to a VOR transmitter.

FIG. 3 is a diagram illustrating a number of parameters utilized inestimating a cone of confusion above a VOR transmitter.

FIG. 4 is a diagram illustrating a number of parameters utilized incalculating a linear deviation from a desired path to a localizertransmitter.

FIG. 5 is a diagram illustrating a number of parameters utilized incalculating a linear deviation from a desired back course path to alocalizer transmitter.

FIG. 6 is a diagram illustrating a number of parameters utilized incalculating a linear deviation from a desired path to a glide slopetransmitter.

FIG. 7 is a flowchart describing a method for determining a lineardeviation from a desired path to a VOR transmitter.

FIG. 8 is a flowchart describing a method for determining a lineardeviation from a desired path to a localizer transmitter.

FIG. 9 is a flowchart describing a method for determining a lineardeviation from a desired glide slope angle.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a block diagram of a portion of a flight guidance system 10according to one embodiment of the present invention. The flightguidance system 10, typically including a flight director and autopilotfunction, includes a microprocessor 12 that is coupled to each of aprogram memory 14, a database 16, pilot controls 18, and a pilot display20. In the embodiment shown, the flight guidance system 10 receivesaircraft position data from GPS receiver 30, which is connected to GPSantenna 32. The flight guidance system 10 also receives inputs from aVHF Omni-directional Range (VOR) receiver 40, which is connected to VORantenna 42. As described above, the VOR system is utilized to navigatefrom VOR transmitter to VOR transmitter along a planned flight path. VORtransmitters are interspersed across a geographic area to providenavigation references for aircraft equipped with VOR receivers 40.

Once an aircraft has navigated past the last VOR transmitter in theplanned flight path, it will begin an approach to an airport, and maybegin to receive signals from an instrument landing system (ILS). As theair vehicle (not shown in FIG. 1) in which the flight guidance system 10is installed approaches the runway for landing, it will receive inputdata from the ILS. An ILS may include a localizer receiver 50, localizerantenna 52, a glide slope receiver 60, and a glide slope antenna 62. Theflight guidance system 10 also receives altitude data 70 from analtitude source, for example, an altimeter corrected for barometricpressure (not shown).

The localizer receiver 50, and the glide slope receiver 60 receivesignals from corresponding transmitters (not shown in FIG. 1). Alocalizer transmitter is located at a far end of a runway and a glideslope transmitter is located at an approach end of the runway. Thelocalizer and glide slope transmitters and receivers (50,60) aid a pilotin properly aligning an aircraft with the runway for landing. Thelocalizer is utilized for a lateral alignment, and the glide slope formaintaining a proper vertical approach angle to the runway.

The database 16 may include location information (i.e. latitude,longitude, and elevation) for each respective VOR transmitter, localizertransmitter, and glide slope transmitter. In addition, runway lengthsand glide path angles are maintained in database 16 for various runways.In one embodiment, data within database 16 relating to VOR transmitterlatitude and longitude are utilized along with aircraft position(latitude and longitude from GPS receiver) to determine a horizontaldistance and bearing to the transmitter. As utilized herein, ahorizontal distance is the distance along the ground between two points.The horizontal distance from the transmitter is utilized along with anangular deviation from a desired flight path, for example from VORreceiver 40, to determine a linear deviation from a desired flight path.Utilizing the linear deviation, the flight guidance system 10determines, for example, pitch and roll commands to steer the vehicle tothe desired flight path.

In the case of VOR, the height above the VOR transmitter, sometimesreferred to as a VOR station, is also utilized to determine a cone ofconfusion for the VOR station, as further described below. Data relatingto runway length for individual runways is stored in database 16 whichis utilized, along with an angular deviation from the desired flightpath provided by localizer receiver 50, to determine a linear deviationfrom a desired lateral approach to a runway. Data relating to glide pathangles for individual runways is also stored in database 16. Such data,along with an angular deviation from the desired glide path angleprovided by glide slope receiver 60, is utilized in determining a lineardeviation from the desired glide path angle to a runway.

FIG. 2 is a diagram illustrating the parameters utilized in calculatinga linear deviation, d, from the desired flight path 102. VOR transmitter100 operates to provide a direction to the transmitter 106, sometimesreferred to as VOR bearing, for an air vehicle 104. The microprocessor12 (shown in FIG. 1) determines the difference between the desiredcourse 102 and the current VOR bearing 106 as an angular deviation 108,denoted as ε. While a pilot would want to change their flight path tothat of the desired course 102, an angular deviation does not providemuch guidance. For example, if air vehicle 104 is 100 miles from the VORtransmitter 100, an angular deviation of three degrees results in alinear deviation 110 in excess of five miles from the desired flightpath 102. However, if air vehicle 104 is only five miles from the VORtransmitter 100, an angular deviation of three degrees results in alinear deviation of about 0.26 miles from the desired flight path 102.From this simple example it is seen that a linear deviation is mostuseful in correcting a flight path of an air vehicle 104.

In one embodiment, for VOR operation, the flight guidance system 10(shown in FIG. 1) uses the VOR transmitter 100 location data stored inthe database 16 along with the current air vehicle position from GPSreceiver 30 to determine a horizontal distance, D, and bearing 106 tothe VOR transmitter 100. This distance is used along with the angulardeviation 108, ε, which is the angular difference between 106 and 102,to determine a linearized deviation 110 from the desired flight path102. The determination of the linear deviation 110 results in improvedflight director and auto pilot tracking. For example, a bank (or turn)angle needed to reduce or eliminate the linear deviation 110 isdisplayed on pilot display 20 (shown in FIG. 1).

Therefore, to linearize the signal from VOR receiver 40, all that isneeded is the horizontal distance to the VOR transmitter 100 and theangular deviation 108, ^(ε), provided by VOR receiver 40. Using datarelating to the VOR transmitter latitude and longitude from database 16along with the GPS data for present latitude and longitude provides thehorizontal distance, D. The resultant linearized deviation is calculatedaccording to: VOR linear deviation=d=D×Sin(^(ε)). Utilizing the lineardeviation, d, the flight guidance system 10 determines roll commands tosteer the vehicle to the desired path 102.

Flight guidance system 10 also utilizes an elevation of VOR transmitter100 from database 16 and barometric altitude data to determine a heightof air vehicle 104 above the VOR transmitter 100. With such data and thehorizontal distance D, flight guidance system 10 is able to determine aconsistent “cone of confusion” extending above the VOR transmitter. Asis further described below, the flight guidance system 10 will use deadreckoning to navigate the air vehicle through the cone of confusion,since the transmitter antenna pattern of VOR transmitter 100 willpreclude stable signals being received by VOR receiver 40 (shown inFIG. 1) in this region.

FIG. 3 illustrates a cone of confusion 150 created by an antenna arraypattern at VOR transmitter 100. To estimate a boundary for the cone ofconfusion 150, a height, H, above the VOR transmitter 100 is required.This height is found by utilization of the elevation data for VORtransmitter 100 from database 16 and the present aircraft baro-correctedaltitude from an air data system (e.g. altitude data 70). The differencebetween the two is the height, H. The cone of confusion is then definedby the ratio of height, H above the station to the distance to thestation, D, as defined above. Determination of whether air vehicle 104is within the cone of confusion 150, and therefore signals originatingfrom VOR transmitter 100 are no longer useful, is a logical expression.If H>D×tan(Cone Angle), where Cone Angle is nominally 60 degrees, thenair vehicle 104 is in the cone of confusion 150, and a pilot shouldutilize dead-reckoning to navigate through the cone, essentially actingas if the linear deviation, d, is zero.

As described above, during VOR transmitter 100 passage (e.g., airvehicle 104 is within the cone of confusion 150) the signals transmittedfrom VOR transmitter 100 are unusable. In an alternative embodiment,instead of dead reckoning to navigate through the cone of confusion 150only using heading information, a better track through the cone ofconfusion 150 is provided if a substituted deviation from GPS isgenerated for the deviation signals received from the VOR transmitter100 during this time.

As also described above, flight guidance system 10 calculates a distanceand bearing to the VOR transmitter 100 using the database values for thetransmitter position of the VOR transmitter 100 and the GPS position ofair vehicle 104. In a specific embodiment, a bearing to the VORtransmitter 100 is calculated as arctan(x/y), if y≧x, and calculated as(90−arctan(y/x)), if x>y (to avoid dividing by zero), where x is thelongitudinal difference (i.e. distance in East-West direction) betweenair vehicle 104 and VOR transmitter 100 and y is the latitude difference(i.e. distance in North-South direction) between the two.

Therefore, the generated bearing data from air vehicle 104 to VORtransmitter 100 is substituted for the deviation based on thetransmitted VOR deviation signals when the signals are insufficient forreception at air vehicle 104, for example, due to a geometry of thetransmitted VOR deviation signal.

FIG. 4 illustrates operation of the localizer portion of the ILS forlinearization of an angular deviation from a desired path, according toanother embodiment of the present invention. As described above, alocalizer transmitter 200 transmits localizer signals which are receivedby localizer receiver 50 which then determines an azimuth, or angularlateral deviation from a desired path 204 to guide the air vehicle 104to the centerline 206 of runway 208. As is shown in FIG. 4, localizertransmitter 200 is located at an end of runway 208 that is opposite anapproaching air vehicle 104.

To determine a linear deviation from desired path 204 utilizing thelocalizer signal, the flight guidance system 10 utilizes the datarelating to location for the localizer transmitter 200 from the database16 along with the current position of air vehicle 104 as determinedthrough GPS receiver 30 to determine a horizontal distance, D, to thelocalizer transmitter 200. This distance, D is utilized along with arunway length, RL, from the database 16, and the angular deviation, ε,as determined by the localizer system (transmitter 200, localizerreceiver 50) into a linear deviation 210, d, with a constant scalefactor to improve auto pilot tracking and performance of the flightguidance system 10.

Specifically, to linearize the deviation from the localizer portion ofthe ILS, an end of runway deviation, y, is first determined throughnormalization of the localizer angular deviation by accounting for theconstant beam width of 350 feet full scale at the threshold (approachend) of all runways. A full scale value (350 feet from a centerline ofthe runway 208 at the end of the runway opposite the localizertransmitter 200) for localizer angular deviation is represented as 0.155DDM (difference in depth of modulation) at an output of the localizerreceiver 50. A difference in depth of modulation occurs because thelocalizer transmitter 200 transmits two modulated signals.

Therefore, an end of runway deviation is calculated as

$y = {{\frac{ɛ}{0.155{DDM}} \times 350\mspace{14mu} {feet}} = {{2258{ɛ({ft})}} = {688.258{{ɛ(m)}.}}}}$

To then determine a linear deviation, d, at the air vehicle 104 from thedesired path 204, the distance D, to localizer transmitter, and thedatabase value for the length of the runway, RL, along with the end ofrunway deviation, y, is are utilized according to

$d = {\frac{D \times y}{\sqrt{{RL}^{2} + y^{2}}}.}$

Such an approach by an air vehicle 104 is sometimes referred to as anILS front course approach.

Sometimes, perhaps due to wind conditions, an aircraft 104 must approachthe runway 208 in a direction that is opposite to the approach directionintended when the localizer transmitter 200 was installed. Such anapproach is sometimes referred to as a back course approach.Determination of a linear deviation from a desired back course approachis illustrated in FIG. 5. During a back course approach, the localizertransmitter 200 is located at the approach end of the runway 208. Asabove, the localizer transmitter 200 transmits localizer signals whichare received by localizer receiver 50 which then determines an azimuth,or angular lateral deviation from a desired path 230 to guide the airvehicle 104 to the centerline 206 of runway 208, albeit from theopposite direction. The linearization equations are the same for backcourse approach as the ILS front course approach described above exceptfor a change in sign.

Therefore, an end of runway deviation is calculated as

$y = {{\frac{ɛ}{0.155{DDM}} \times 350\mspace{14mu} {feet}} = {{2258{ɛ({ft})}} = {688.258{{ɛ(m)}.}}}}$

To then determine a linear deviation 232, d, at the air vehicle 104 fromthe desired path 230, the distance D, to the localizer transmitter, andthe database value for the length of the runway, RL, along with the endof runway deviation, y, are utilized according to

$d = {\frac{D \times y}{\sqrt{{RL}^{2} + y^{2}}}.}$

Similar to passage of VOR transmitter 100 through the cone of confusion150 described above, the signal from the localizer transmitter 200sometimes cannot be used by air vehicle 104. One such example is whenthe air vehicle 104 is far enough away from the desired path 204 thatthe output of localizer receiver 50 reaches a maximum value (also knownas saturation). In such a case, a capture cannot be calculated bylocalizer receiver 50 because there is no sense of deviation rate fromthe transmitted localizer signal. This causes the flight guidance systemto wait until the receiver output is no longer saturated before startinga turn to acquire the localizer signal. This may be too late for thelimited bank angles utilized by the flight guidance system. Such latecapture of the localizer signal can sometimes result in an overshoot ofthe desired path 204 by air vehicle 104. Sometimes the overshoot by airvehicle 104 is significant and a resultant position of air vehicle 104is quite a distance from the desired path 204.

In an alternative embodiment, flight guidance system 10 is configured tocause a capture of the transmitted localizer signal when the transmittedlocalizer signal from the localizer transmitter 200 cannot be capturedby localizer receiver 50, based on a derived deviation from desired path204. Utilizing the derived deviation from desired path 204, air vehicle104 is able to begin turning at a location (referred to herein as acapture point) which will allow the localizer signal to be acquiredwithout significantly overshooting the desired path 204.

Similar to the calculation of a derived bearing to VOR transmitter 100described above, flight guidance system 10 determines a distance andbearing to the localizer transmitter 200 using the database values forthe transmitter position of the localizer transmitter 200 and the GPSposition of air vehicle 104. This bearing and distance information isused to calculate a substitute deviation from the desired path 204,which provides the information necessary to capture and acquire thelocalizer while the receiver is in saturation. In a specific embodiment,a bearing to the localizer transmitter 200 is calculated as arctan(x/y),if y≧x, and calculated as (90−arctan(y/x)), if x>y (to avoid dividing byzero), where x is the longitudinal difference between air vehicle 104and localizer transmitter 200 and y is the latitude difference betweenthe two.

Therefore, the bearing data from air vehicle 104 to the desired path 204to localizer transmitter 200 is utilized in conjunction with thedistance data between the two to calculate a deviation that substitutesfor the transmitted localizer deviation signal when the signal issaturated, which means that the signal is insufficient for reception atair vehicle 104. The calculated deviation signal augments thetransmitted localizer signals and allows capture of the transmittedlocalizer signals under situations, for example high speeds andintercept angles, when a capture based on the transmitted localizersignals occurs too late to avoid an overshoot.

FIG. 6 illustrates operation of the glide slope portion of the ILS.Specifically, to determine a linear deviation from the glide slope path250, the flight guidance system 10 uses data relating to a location forthe glide slope transmitter 252 from the database 16 along with thecurrent aircraft position from GPS receiver 30 to determine a horizontaldistance, D, to the glide slope transmitter 252. This horizontaldistance, D, is used along with the glide path angle 254 from thedatabase 16 to convert an angular altitude deviation signal receivedfrom glide slope receiver 60 into a linearized deviation, d, 256 with aconstant scale factor to improve autopilot tracking and operation offlight guidance system 10.

To linearize the angular error from the glide path angle utilizing theglide slope portion of the ILS, the distance, D, to the glide slopetransmitter 252 is used. The distance, D, is determined as thedifference between air vehicle position, provided by GPS receiver 30 anddata relating to the location of the glide slope transmitter 252 fromdatabase 16. In one embodiment, the database 16 does not include datarelating to a position of the glide slope transmitter 252. Rather, insuch an embodiment, data relating to a position of the localizertransmitter 200 along with data relating to runway length are utilizedto estimate a position of the glide slope transmitter 252.

The glide path angle, GPA, stored in database 16, and height above thestation, H, which is derived from the transmitter 252 elevation indatabase 16, and elevation of air vehicle 104 (from either a GPS or anair data computer 70 (shown in FIG. 1)) are utilized to determine if anunwanted side lobe of the glide slope signal is being received, asopposed to the desired main beam. This determination of main/side lobehelps to prevent false captures.

FIG. 6 shows the geometry of the linearization, where ε is the GSdeviation error in DDM, and the full scale (F.S.) value for glide slopedeviation is represented as 0.175DDM at the glide slope receiver 60output, corresponding to 0.2×GPA from the database 16. The glide slopedeviation error angle in radians is

${\alpha = {\frac{ɛ}{0.175{DDM}} \times 0.2{GPA}}},$

and the glide slope linear deviation is

$d = {\frac{D}{\cos \left( {{GPA} - \alpha} \right)} \times {{\sin (\alpha)}.}}$

If (0.75×GPA)<arctan(H/D)<(1.5×GPA), then capture is allowed.

The above described calculation of deviation signals that substitute forthe transmitted localizer deviation signal and calculation of a capturepoint for the transmitted localizer signals along a desired path arealso applicable to capture of glide slope transmitter transmissionsusing the same methodology.

FIG. 7 is a flowchart 300 illustrating the methods disclosed herein forlinearizing a deviation from a VOR bearing signal. Referring toflowchart 300, a pilot selects 302 a flight course. Flight guidancesystem 10 (shown in FIG. 1) receives 304 a VOR bearing from the VORreceiver 40 (shown in FIG. 1). The flight guidance system 10 retrieves306 a position (i.e. latitude, longitude, and elevation) of the VORtransmitter 100 (shown in FIG. 2). The flight guidance system 10 thenreceives 308 a vehicle position (i.e. latitude, longitude, andelevation) from a GPS receiver 30 (shown in FIG. 1). The flight guidancesystem 10 calculates 310 a linear deviation from the VOR bearingutilizing the methodology described with respect to FIG. 2. Uponcalculation 310 of the linear deviation, the flight guidance system 10is configured to calculate 312 a roll command that corresponds to a rollthat is needed to minimize the deviation from the VOR bearing signal.The pilot then decides 314 whether the roll command is to be executedmanually or through an auto pilot system.

FIG. 8 is a flowchart 350 illustrating the methods disclosed herein forlinearizing a deviation from a center of a localizer signal that is aportion of the functionality provided by an ILS. The method is similarto that associated with determining a linear deviation from a VORbearing (shown in FIG. 7). Referring to flowchart 350, a pilot selects352 a flight course. Flight guidance system 10 (shown in FIG. 1)receives 354 localizer data from the localizer receiver 50 (shown inFIG. 1). The localizer data is in the form of a deviation from a nullbetween the localizer's transmitted beams. The flight guidance system 10retrieves 356 a position (i.e. latitude, longitude, elevation, andrunway length) of the runway associated with the localizer transmitter200 (shown in FIG. 4). The flight guidance system 10 then receives 358 avehicle position (i.e. latitude, longitude, and elevation) from a GPSreceiver 30 (shown in FIG. 1). The flight guidance system 10 calculates360 a linear deviation from the localizer signal utilizing themethodology described with respect to FIG. 4. Upon calculation 360 ofthe linear deviation, the flight guidance system 10 is configured tocalculate 362 a roll command that corresponds to a roll that is neededto minimize the deviation from the localizer signal. The pilot thendecides 364 whether the roll command is to be executed manually orthrough an auto pilot system. A method similar to that illustrated byflowchart 350 is utilized in determining a linear deviation from adesired path for a back course approach to a runway.

FIG. 9 is a flowchart 400 illustrating the methods disclosed herein forlinearizing an angular altitude deviation from the ILS glide path. Theglide slope angular altitude deviation is a portion of the functionalityprovided by an ILS. The method is similar to that associated withdetermining a linear deviation from a VOR bearing (shown in FIG. 7).Referring to flowchart 400, flight guidance system 10 (shown in FIG. 1)receives 404 a glide slope error angle from the glide slope receiver 60(shown in FIG. 1). The flight guidance system 10 retrieves 406 aposition (i.e. latitude, longitude, elevation) and a glide path anglethat is defined for the runway associated with glide slope transmitter252 (shown in FIG. 6). The flight guidance system 10 then receives 408 avehicle position (i.e. latitude, longitude, and elevation) from a GPSreceiver 30 (shown in FIG. 1). The flight guidance system 10 calculates410 a linear deviation from the glide path angle utilizing themethodology described with respect to FIG. 6. Upon calculation 410 ofthe linear deviation, the flight guidance system 10 calculates 412 apitch command that is needed to reduce the deviation from the glide pathangle. The pilot then decides 414 whether the pitch command is to beexecuted manually or through an auto pilot system.

The described systems and methods are able to achieve improvedperformance over classical methods, due to the use of GPS position dataand database values for transmitter positions.

While the invention has been described in terms of various specificembodiments, those skilled in the art will recognize that the inventioncan be practiced with modification within the spirit and scope of theclaims.

1. A method for providing a bearing from a vehicle to a transmittingstation, said method comprising: accessing a database to obtaintransmitter position information for the transmitting station; obtainingvehicle position information based on a GPS signal; generating thebearing from the vehicle to the transmitting station utilizing thetransmitter position information and the vehicle position information;identifying when the vehicle is in a VOR cone of confusion extendingfrom the transmitting station based on the transmitter positioninformation and the vehicle position information; and calculating anestimated deviation representing a deviation from a desired course tothe transmitting station using the bearing from the vehicle to thetransmitting station.
 2. The method according to claim 1, wherein theaccessing obtains transmitter position information for the location ofat least one of a VOR transmitter, a localizer transmitter of aninstrument landing system (ILS), and a glide slope transmitter of theILS.
 3. The method according to claim 1, further comprising: determininga distance to the transmitting station; and calculating a deviationrepresenting a deviation from a desired course to the transmittingstation using the distance and the bearing from the vehicle to thetransmitting station.
 4. The method according to claim 1, furthercomprising: determining a distance to the transmitting station;calculating a deviation representing a deviation from a desired courseto the transmitting station using the distance and the bearing from thevehicle to the transmitting station; and utilizing the calculateddeviation in connection with control of the vehicle when the signalsfrom the transmitting station are of insufficient strength to becaptured by a signal receiver.
 5. The method according to claim 1,wherein generating the bearing comprises: determining vehicle latitudeand longitude from the vehicle position information and transmittingstation latitude and longitude from the vehicle position information;and calculating a bearing to the transmitting station from thedifferences between the vehicle and transmitting station latitudes andlongitudes.
 6. The method according to claim 1, further comprisingcalculating a flight director roll command utilizing the bearing fromthe vehicle to the transmitting station.
 7. The method according toclaim 1, further comprising initiating a flight director roll command toan auto-pilot function utilizing the bearing from the vehicle to thetransmitting station.
 8. The method according to claim 1, wherein thetransmitting station is a localizer transmitter, and wherein generatingthe bearing comprises: calculating a deviation from a desired path tothe localizer transmitter using the vehicle position information; andusing the deviation to calculate a bearing to a capture point for thesignals transmitted from the localizer transmitter.
 9. The methodaccording to claim 1, wherein the transmitting station is a glide slopetransmitter, and wherein generating the bearing comprises: calculating adeviation from a desired path to the glide slope transmitter using thevehicle position information; and using the deviation to calculate abearing to a capture point for the signals transmitted from the glideslope transmitter.
 10. A method for providing a bearing from a vehicleto a transmitting station, said method comprising: accessing a databaseto obtain transmitter position information for the transmitting station;obtaining vehicle position information based on a GPS signal;calculating a deviation from a desired path to the transmitting stationusing the vehicle position information and the transmitter positioninformation; and using the deviation to calculate a bearing to a capturepoint for the signals transmitted from the transmitting station.
 11. Themethod of claim 10, wherein the transmitting station is at least one ofa localizer transmitter and a glide slope transmitter and the accessingincludes accessing a database including transmitter position informationfor a plurality of localizer transmitters and glide slope transmitters.12. The method according to claim 10, further comprising: determining adistance to the transmitting station; and calculating a deviationrepresenting a deviation from a desired course to the transmittingstation using the distance and the bearing from the vehicle to thetransmitting station.
 13. The method according to claim 10, furthercomprising: determining a distance to the transmitting station;calculating a deviation representing a deviation from a desired courseto the transmitting station using the distance and the bearing from thevehicle to the transmitting station; and utilizing the calculateddeviation in connection with control of the vehicle when the signalsfrom the transmitting station are of insufficient strength to becaptured by a signal receiver.
 14. The method according to claim 10,further comprising calculating a flight director roll command utilizingthe bearing from the vehicle to the transmitting station.
 15. The methodaccording to claim 10, further comprising initiating a flight directorroll command to an auto-pilot function utilizing the bearing from thevehicle to the transmitting station.
 16. The method according to claim10, wherein said generating partitions processing among multipleprocessors to generate the bearing and a resulting flight directorcommand.